1. Field of the Invention
The present invention relates to a pattern transfer method.
2. Description of the Related Art
Nano-imprinting, a type of microprocessing technology that has been attracting a great deal of interest in recent years, is a technology whereby an indentation/projection (relief) pattern is transferred onto a substrate by using a mold having a fine relief pattern formed thereupon (see nonpatent reference literature: Spectroscopic Research vol 51, #4 (2002)). FIGS. 10A-10H illustrate a nano-imprinting method that may be adopted for pattern transfer. A substrate 110 having formed thereupon a resist film 120 is first prepared (see FIG. 10A).
Next, a mold 140 with a relief pattern formed thereupon is prepared and the surface of the mold 140 with the relief pattern is pressed against the resist film 120, thereby deforming the resist film 120 (see FIG. 10B). The mold 140 having been pressed against the resist film 120 is then separated from the resist film 120 (see FIG. 10C). The relief pattern at the mold is transferred onto the resist film 120 as a result.
Then, the residual resist 125 present over the area having been compressed by the mold 140 is removed through dry etching, thereby exposing the surface of the substrate 110 over the area (see FIG. 10D). Subsequently, a metal film 130 constituted of Ni or the like is vapor-deposited onto the substrate 110 (see FIG. 10E)). The resist film 120 is next removed by using an organic solvent (see FIG. 10F). Thus, only the metal film 130 having been directly deposited onto the substrate 110 remains on the substrate 110.
Using the remaining metal film 130 as a mask pattern, the surface of the substrate 110 is etched to a predetermined depth through an optimal etching method (see FIG. 10G). The metal film 130 is then removed from the etched substrate and, as a result, the substrate 110 with the relief pattern at the mold 140 transferred thereon is obtained (see FIG. 10H).
When transferring a pattern through nano-imprinting by using a resist as described above, the pattern cannot be sustained if it is transferred before pre-baking the resist. If the resist is to be pre-baked during the transfer, the mold needs to be formed by using a material that will withstand the baking process, which is bound to impose limitations on the choice of the material. Thermal deformation, which will prevent high-precision pattern transfer, is another problem that needs to be considered. Pattern transfer after the pre-baking process, on the other hand, is problematic in that the resist will have become hardened through the pre-baking process and thus the pattern cannot be transferred readily.
As an alternative to the resist, a resin may be used. The use of resin facilitates transfer of a curved pattern, e.g., a lens, which cannot be transferred with ease using a resist. However, it is difficult to reliably remove the resin following the etching process, leading to a problem of residual resin left on the substrate 110. The resin may be removed through, for instance, oxygen plasma ashing but it is still difficult to remove the resin reliably.